8.4 The most important events in the third to eighth developmental weeks

Seventh week
(stages 18 to 20; ca. 44-49 days)


Quiz 02

Numerous changes to the embryo's limbs happen in this week. The places where finger and toes arise become visible.

The interdigital necrosis zones (INZ) are also now clearly recognizable in the lower extremities 18.

The heart musculature differentiates.

Hematopoiesis begins in the liver 18.

The physiologic umbilical hernia is still present.

The ossification of the upper extremities has already begun. The head becomes rounded, raises and looks more and more human.

The cloacal membrane tears 19.


Embryo ca. 44 days
(stage 18)


Embryo ca. 46 days
(stage 19)


Embryo ca. 49 days
(stage 20)

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